Open Shortest Path First
The most basic of terms that are related to OSPF are related to many routing
protocols. We begin by defining relationships among routers. From there, we
will move on to defining terms relating to OSPF operations.
Neighbor A neighbor refers to a connected (adjacent) router that is run-
ning an OSPF process with the adjacent interface assigned to the same
area. Neighbors are found via Hello packets. No routing information is
exchanged with neighbors unless adjacencies are formed.
Adjacency An adjacency refers to the logical connection between a
router and its corresponding designated routers and backup designated
routers. The formation of this type of relationship depends heavily on the
type of network that connects the OSPF routers.
Link In OSPF, a link refers to a network or router interface assigned to
any given network. Within OSPF, link is synonymous with interface.
Interface An interface is the physical interface on a router. When an
interface is added to the OSPF process, it is considered by OSPF as a link.
If the interface is up, then the link is up. OSPF uses this association to
build its link database.
Link State Advertisement Link State Advertisement (LSA) is an OSPF
data packet containing link-state and routing information that is shared
among OSPF routers.
Designated router A designated router (DR) is used only when the
OSPF router is connected to a broadcast (multi-access) network. To min-
imize the number of adjacencies formed, a DR is chosen to disseminate/
receive routing information to/from the remaining routers on the broad-
cast network or link.
Backup designated router A backup designated router (BDR) is a hot
standby for the DR on broadcast (multi-access) links. The BDR receives
all routing updates from OSPF adjacent routers but does not flood LSA
OSPF areas OSPF areas are similar to EIGRP Autonomous Systems.
Areas are used to establish a hierarchical network. OSPF uses four types
of areas, all of which will be discussed later in this chapter.
Copyright ©2001 SYBEX , Inc., Alameda, CA